Reyes hit the game-winning infield single with two outs in the bottom in the ninth inning when Rosenthal was late covering first base as the Mets edged the Cardinals 3-2 on Thursday afternoon.
"I saw the first baseman playing way back and I said in my mind if you hit something there, you know, hustle to first base and when I see the pitcher, he was standing on the mound for like two seconds and I said, man, it's going to be tough for him to beat me to first base," Reyes said.
The Mets had runners at first and third following singles by Yoenis Cespedes and T.J. Rivera. One pitch after Rivera singled, Reyes gave the Mets the win in a game decided by who executed a fundamental play better.
Carpenter was playing behind the bag and near the foul line. He fielded the sharply hit grounder, spun around to make a throw from foul territory but Rosenthal wasn't there.
Carpenter then attempted to make the play himself but by then Reyes already slid in head first. When Rosenthal arrived, the right-hander had to leap over Reyes to avoid a collision after initially thinking Carpenter was going to make the out himself.
"For a split second, I thought he might," Rosenthal said. "But looking back on it, he was pretty deep. I wish I would have maybe got a throw or maybe a chance to tag him or something. It's a fundamental play, a PFP (pitcher's fielding practice). If we expect guys to play defense behind us, we've got to do our part too."
Reyes' hustle gave the Mets their third walkoff win of the season and their fifth win in the last 13 games. It was the shortstop's fourth career game-ending RBI and it touched off a wild celebration near first base once Cespedes scored the winning run.
"First thing I saw was if the ball was fair and then I tried to see where the pitcher was, because I knew Jose was busting it down the line and when I saw the pitcher wasn't there I knew he was going to beat it out," Mets manager Terry Collins said.
The Cardinals were unable to win three of four after outscoring the Mets 11-3 in the first two games of the series and fell to 3-4 on a 10-game road trip before heading to Wrigley Field for a series with the surging Chicago Cubs.
"You got to get over," Carpenter said. "I turned and looked to throw and he's nowhere close."
It was the second time Rosenthal did not cover but unlike the time he did not cover for Anthony Rendon's potential game-ending double play July 1, the Cardinals did not escape with a win this time.
Before Reyes hustled and Rosenthal did not execute, the teams traded solo homers in the eighth.
Tommy Pham slugged his 13th homer into the left-field seats with one out against Erik Goeddel to give St. Louis a 2-1 lead. Pinch hitter Wilmer Flores tied the game with a homer over the left-center field fence against left-hander Brett Cecil.
The Mets nearly began a rally after Flores hit his third career pinch-hit homer but Curtis Granderson's infield single was overturned when the Cardinals challenged the initial ruling.
After the Mets were unable to regain the lead, Addison Reed (1-2) pitched a scoreless ninth.
Before the late-inning hits, neither did team much offensively.
Lucas Duda homered off Lance Lynn for the Mets while Pham hit a run-scoring double for St. Louis.
Pham's double occurred an inning after Seth Lugo lost his no-bid by allowing a two-out single to right by Greg Garcia.
Lugo allowed one run and four hits in 6 2/3 innings while throwing a career-high 103 pitches. Lynn allowed one run and four hits in six innings.
The Mets took a 1-0 lead when Duda hit a full count fastball over the right field wall to start the second. The Cardinals tied it when Carpenter walked and scored on Pham's double with one out in the sixth.
NOTES: Mets manager Terry Collins said he spoke to 2B/SS Asdrubal Cabrera about fielding ground balls at third base in preparation of a potential move there. Collins said Cabrera would not play third until 2B Neil Walker returns from a hamstring injury. ... St. Louis RHP Lance Lynn had his 14 1/3 scoreless inning streak end when 1B Lucas Duda homered in the second. ... The Mets activated RHP Josh Smoker from the disabled list and designated RHP Neil Ramirez for assignment. Ramirez was designated by his third team this season after being cut by the Toronto Blue Jays and San Francisco Giants in May. ... St. Louis LF Tommy Pham fouled a ball off his left leg in the fourth inning but stayed in the game.